The present invention relates to semiconductor device, and more specifically, to carbon nanotube (CNT) semiconductor devices.
Semiconductor devices having a robust self-aligned device structure are desirable when fabricating carbon nanotube field-effect transistors (CNTFETs). The robust self-alignment configuration is technologically relevant for highly integrated digital applications. For example, self-aligned devices improve uniformity of key parameters such as parasitic capacitance, thus enabling uniform operation of the transistors across a chip.
Self-aligned CNTFETs are typically fabricated by leveraging a pre-formed gate region as a mask when performing ion implantation to form the source and drain contacts. Since the gate serves as the mask, the source and drain contacts are formed in direct and consistent proximity to the gate, thereby providing a self-aligned CNTFET device. Current trends in self-aligned CNTFET devices have led to the implementation of doped extensions to enhance carrier injection into the channel, which in turn improves on-state performance. Enhanced carrier injection into the channel also suppresses ambipolar conduction, i.e., reduces ambipolar diffusion of carriers from the channel, so as to improve off-state device performance. As the size of CNTFET devices continue to decrease, however, it has become more difficult to maintain the uniformity of smaller doped extensions using conventional fabrication processes.